The invention relates to an ignition device for an extraneously igniting combustion piston engine and a combustion piston engine with such an ignition device.
In current extraneously igniting combustion piston engines such as in particular the spark-ignited engines used in motor vehicle construction, the combustion of the petrol-air mixture normally starts from substantially one point, e.g. from the ignition point of a spark plug. The ignition gaps of such spark plugs are extremely small, in particular in order to keep the necessary ignition voltage low. However, such construction designs mean that the combustion of the petrol-air mixture spreads substantially from a point of a clearly larger ignition chamber of the cylinder and possibly—particularly in the case of high engine speeds—the combustion process is not concluded when the mixture is blown out of the cylinder.
By reason of the associated incomplete combustion of the mixture in the cylinder, the entire heating value of the mixture cannot be converted into torque, which has a negative influence on the degree of efficiency of the engine. In addition, the exhaust tract subjected to heavy thermal loading by reason of afterburning processes, whereby more intensive demands are placed on the design of this exhaust tract in terms of installation space and/or cost, especially with respect to the cooling thereof and/or separate heat protection measures.
In order to remedy this problem, in the past “spark-to-piston” designs for spark-ignited engines have been proposed, in which the ignition gap is formed by an electrode on the cylinder head and an electrode on the piston. However, the longer ignition gap associated therewith requires a clearly higher ignition voltage than for commercially available spark plugs, which voltage then must also be present at the electrode on the piston. However, this means that complex electrical isolation of the piston is required, which is difficult to achieve by reason of the components of the piston guide which are moved in a highly dynamic manner with respect to each other. In any case, such isolation is associated with high costs and possibly with compromises in terms of other performance parameters.